In the 1944 film Gaslight, Charlie Boyer’s character tries to convince his wife, played by Ingrid Bergman, that she is going insane. He manufactures circumstances that challenge what Bergman knows to be true, such as whether the eponymous gaslights in the house are flickering. In modern usage, “gaslighting” usually refers to a form of abuse: one person in a relationship subtly influencing the other to doubt their own reality. It’s a power thing. It is not lit.